Lectrosonics IFBT423A User Manual
IFBT4
Synthesized UHF IFB Transmitter
INSTRUCTION MANUAL
Featuring Digital Hybrid Wireless™ Technology
U.S. Patent 7,225,135
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Purchase Date:
Rio Rancho, NM, USA
www.lectrosonics.com
IFBT4
2
LECTROSONICS, INC.
Multi-Frequency IFB Transmitter
Table of Contents
General Technical Description ..............................................................................................................................................................4
Introduction ...........................................................................................................................................................................................4
Audio Input Interface .............................................................................................................................................................................4
Input Limiter ..........................................................................................................................................................................................4
Audio DSP and Noise Reduction ..........................................................................................................................................................5
Pilot Tone Squelch System ...................................................................................................................................................................5
Frequency Agility...................................................................................................................................................................................5
Power Delay ..........................................................................................................................................................................................5
Microcontroller ......................................................................................................................................................................................5
Transmitter ............................................................................................................................................................................................5
Antenna System ....................................................................................................................................................................................5
Front Panel Controls and Functions .....................................................................................................................................................6
IFBT4 Front Panel ................................................................................................................................................................................. 6
OFF/TUNE/XMIT Switch .......................................................................................................................................................................6
Power Up Sequence .............................................................................................................................................................................6
Main Window .........................................................................................................................................................................................6
Frequency Window................................................................................................................................................................................6
Audio Input Gain Window ...................................................................................................................................................................... 6
Setup Window .......................................................................................................................................................................................6
ROLLOFF Setup Screen .......................................................................................................................................................................6
COMPAT Setup Screen ......................................................................................................................................................................... 7
TUNING Setup Screen .........................................................................................................................................................................7
Lock/Unlock Panel Buttons ................................................................................................................................................................... 7
IFBT4 Menu Diagram ............................................................................................................................................................................7
Rear Panel Controls and Functions ......................................................................................................................................................9
IFBT4 Rear Panel .................................................................................................................................................................................9
XLR Jack ...............................................................................................................................................................................................9
MODE Switches ....................................................................................................................................................................................9
Power Input Connector .........................................................................................................................................................................9
Antenna .................................................................................................................................................................................................9
Installation and Operation ...................................................................................................................................................................10
Operating Notes ....................................................................................................................................................................................10
Accessories ..........................................................................................................................................................................................11
Troubleshooting ....................................................................................................................................................................................12
Frequency Blocks and Ranges ...........................................................................................................................................................13
UHF Transmitter Antenna Specifications ............................................................................................................................................13
Specifications .......................................................................................................................................................................................14
Service and Repair ...............................................................................................................................................................................15
Returning Units for Repair ..................................................................................................................................................................15
Rio Rancho, NM
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IFBT4
XMIT
General Technical Description
Introduction
The IFBT4 IFB transmitter brings DSP capability and a
convenient LCD interface to the popular Lectrosonics
IFB product line. Replacing the venerable IFBT1 transmitter, the IFBT4 retains the same physical size and is
fully interchangeable with its predecessor in terms of
audio, RF and power interfaces. Along with providing
peerless audio quality with wide frequency response
and dynamic range in Nu Hybrid mode, the technology used in the IFBT4 includes compatibility modes for
Lectrosonics Mode 3 and IFB receivers.
The IFBT4 features a graphics type backlit LCD display
with a menu system similar to those featured in our 400
Series receivers. The IFBT4 can be “Locked” to prevent
a user from changing any settings but still allow browsing of the current settings.
The IFBT4 can be powered from any external DC
source of 6 to 18 Volts at 200 milliamps maximum or
from the provided 12 Volt power supply with a locking
power connector. The unit has an internal self-resetting
fuse and reverse polarity protection.
The IFBT4 is housed in a machined aluminum case
with a tough electrostatic powder coating. The front and
rear panels are anodized aluminum with laser etched
engraving. The included antenna is a right angle, ¼
wavelength monopole with a BNC connector, constructed of polymer coated flexible steel cable.
These features, along with the 250 milliwatt RF output
and a wide range of selectable audio input types and
levels, make the IFBT4 an excellent choice for long
range IFB applications and other long range wireless
audio needs.
IFBT4 Transmitter
Audio Input Interface
The standard 3 pin XLR connector on the rear panel
handles all audio inputs. The four DIP switches allow
setting the input sensitivity for low levels, such as microphone inputs, or for high levels, such as line inputs, balanced or unbalanced. The switches also offer special
settings to provide the proper input configurations to
match to Clear Com, RTS1, and RTS2 intercom systems. Pin 1 of the XLR input connector is normally connected to ground but an internal jumper can be moved if
a floating input is desired.
While the XLR input does not offer phantom power, it is
fully compatible with standard 48 Volt phantom power.
Phantom supplied microphones may be connected to
the IFBT4 without the need for DC isolation.
A user-selectable low frequency roll-off can be set for
35 Hz or 50 Hz. The recommended 50 Hz default setting helps to remove wind and traffic noise, air conditioner rumble, and other sources of undesired low
frequency audio. The 35 Hz setting offers a fuller range
of sound in the absence of adverse conditions.
Input Limiter
A DSP-controlled analog audio limiter is employed
before the analog-to-digital converter. The limiter has a
range of more than 30 dB for excellent overload protection. A dual release envelope makes the limiter acoustically transparent while maintaining low distortion. It can
be thought of as two limiters in series: a fast attack and
Block Diagram
Audio Input Interface
XLR
Input
Power
Input
6-18VDC
200mA
+
-
Polyfuse
Connector
3
Voltage
Regulator
Power
OFF
TUNE
Mode
2
1
Set
Switches
(Rear
Panel)
Graphic LCD Display
Front
Panel
Controls
Input
Amplifier
UP
DOWN
MENU
+5 V
+3.3 V
+1.8 V
-5 V
Shunt
Limiter
LF
Roll-Off
Phase Locked Loop
11.3 MHz
Reference
Input
Amp
Audio
Level
Audio
4
A-D
Converter
11001001 11001001
Digital Signal Processor
Microprocessor
D-A
Converter
Voltage
Controlled
Oscillator
Filter
Amp
11.3 MHz
Reference
Final
Amplifier
Isolator
50
LECTROSONICS, INC.
Multi-Frequency IFB Transmitter
release limiter followed by a slower attack and release
limiter. The dual release limiter recovers quickly from
brief transients but recovers more slowly from sustained
high levels, keeping audio distortion low while preserving short term dynamic changes. When the audio
meter on the LCD display widens slightly as it reaches
zero, limiting is indicated. When the zero changes to a
letter C, severe limiting and/or clipping is indicated.
Audio DSP and Noise Reduction
Lectrosonics IFB systems use a single band compandor and pre-emphasis for exceptional IFB audio quality.
The IFBT4 performs these traditionally analog functions
entirely in the digital domain, maintaining historical
compatibility while requiring fewer adjustments. When
the IFBT4 is configured for compatibility with other
types of wireless systems, the DSP stops IFB companding and instead performs the appropriate audio
processing for the chosen mode. The Nu Hybrid mode
offers objectively superior audio performance and is
recommended when the receiver is capable of supporting it.
Pilot Tone Squelch System
Lectrosonics IFB systems use a special “pilot tone” so
that valid IFB signals can be distinguished from RF
interference. During normal operation, an IFB receiver
will listen for the distinctive pilot tone, remaining silent
(squelched) until the pilot tone is detected. The pilot
tone is located well above audio frequencies and is
never passed through to the receiver’s audio output.
The benefit of the pilot tone squelch system is that the
receiver will remain muted until it receives the pilot tone
from the matching transmitter, even if a strong interfering RF signal is present on the carrier frequency of the
system.
When the IFBT4 is operated in compatibility modes
other than IFB, it generates pilot tones as appropriate
for the chosen mode.
Power Delay
When powering the transmitter on and off, and when
switching between the XMIT and TUNE modes, intelligent circuitry adds brief delays in order to allow time
for circuits to stabilize, both locally and in the matching
receiver. These delays prevent clicks, thumps or feedback from entering the sound system.
Microcontroller
The microcontroller oversees most system operations,
including RF frequency and output, DSP audio functions, buttons and display, and more. User settings
are stored in non-volatile memory, so they are retained
even when the power is turned off.
Transmitter
The IFBT4 transmitter operates at a high RF power
level to ensure a clean signal free of dropouts and
noise. All transmitter circuits are buffered and filtered
for excellent spectral purity. The IFBT4’s clean signal
reduces the chances for interference in multiple transmitter installations.
Antenna System
The 50 Ohm BNC output connector will work with standard coaxial cabling and remote antennas.
Frequency Agility
The IFBT4 transmitter uses a synthesized, frequency
selectable main oscillator. The frequency is extremely
stable over a wide temperature range and over time.
The transmitter’s standard tuning range covers 256 frequencies in 100 kHz steps over a 25.6 MHz band. This
flexibility significantly helps avoid interference problems
in mobile or traveling applications.
Rio Rancho, NM
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